Detection of occult tumor cells in peripheral blood from patients with small cell lung cancer by reverse transcriptase-polymerase chain reaction

The reverse transcriptase-polymerase chain reaction (RT-PCR) of tumor-speci fic or -associated genes is a sensitive assay for detecting a,minimal numbe r of tumor cells in peripheral blood (PB) or bone marrow (BM). In this stud y, we determined whether mRNA of bombesin receptors is detectable in PB or peripheral blood progenitor cell (PBPC) samples from patients with small ce ll lung cancer Among three bombesin-like peptide receptors, we used the neu romedin B receptor (NMB-R) gene as a target, because of the most frequent e xpression on SCLC cell lines. The lower limit of detection was one tumor. c ell in one million normal PB cells and there was no detection in normal PB or BM cells unlike a cytokeratin 19 gene. The NMB-R gene was detected in 14 (31.8 %) of 44 PB samples from patients with SCLC at diagnosis and 2 (15.4 %) of 13 samples of PBPC collected during a recovery phase after chemother apy followed by administration of G-CSF (filgrastim). At diagnosis, patient s whose PB was positive for the NMB-R gene had a significantly shorter surv ival than those who were negative. Our observation suggests that this assay may be useful in diagnosing metastatic disease and monitoring minimal resi dual disease in patients with SCLC.